1. Field of the Invention
The present invention relates to a semiconductor holding apparatus for holding a semiconductor substrate in semiconductor processing equipment and, more particularly, to a structure of a susceptor for holding a substrate in plasma CVD equipment.
2. Description of the Related Art
Plasma CVD equipment is commonly used for exciting a particular source gas in an evacuated reaction chamber using high-frequency plasma to deposit a thin film on a semiconductor substrate. Reaction products similar to those on the surface of a semiconductor wafer are deposited on the inner wall of the reaction chamber of such plasma CVD equipment. It is therefore necessary to perform plasma etching periodically using a gas including fluorine atoms to eliminate the reaction products for cleaning in order to prevent contamination of a semiconductor wafer. In doing this, a susceptor is required above all to be resistant to fluorine so that it does not react with fluorine active species to generate a contaminant. Since it is also required to heat a semiconductor substrate rapidly to a predetermined temperature, high thermal conductivity is also required.
Anodized susceptors made of aluminum or aluminum alloy incorporating a high-frequency electrode have been widely used as substrate holding apparatuses for holding a substrate in plasma CVD equipment. However, a problem has existed in that the surface of an anodized susceptor is liable to cracks in a plasmatic environment at 400.degree. C. and in that fluorine active species penetrate into the cracks to corrode aluminum inside.
Under such circumstances, susceptor devices such as that disclosed in U.S. Pat. No. 5,558,717 have been developed which have a structure wherein a mount plate made of aluminum nitride for mounting a semiconductor substrate is put in contact with an upper surface of a heating block made of high purity aluminum with a nichrome wire embedded therein. Such conventional susceptors were developed to take advantage of the fact that ceramic materials such as aluminum nitride are resistant to fluorine based active species and are excellent in thermal conductivity.
However, such conventional susceptors face a difficulty in mechanically attaching and fixing their components due to distortions attributable to the fact that two types of materials, i.e., aluminum nitride and high purity aluminum, having significantly different thermal expansion coefficients are put in contact with each other. As a result, a problem arises in that there will be imperfect contact regions into which active species of fluorine can penetrate to corrode the top surface of the heating block, thereby generating a contaminant.
Further, the part of the heating block of such conventional susceptors can react with fluorine active species to generate a contaminant because it is made of aluminum.
Since the susceptors also serve as high-frequency electrodes, such imperfect contact can produce a parasitic capacity which can adversely affect the distribution of high-frequency discharge.
Furthermore, the conventional susceptors have a problem in that their manufacturing cost is high and the operating cost of an apparatus is therefore increased.
It is therefore an object of the invention to provide a substrate holding apparatus having a mount surface which is highly resistant to fluorine based active species and free from the risk of contamination by impurities.
It is another object of the invention to attach a mount plate and a heating block to each other with perfect tightness to eliminate any gap through which fluorine active species can enter, thereby improving resistance to fluorine and improving thermal conductivity to improve process stability.
It is still another object of the invention to shield a heating block from fluorine active species completely, thereby improving the resistance of a substrate holding apparatus as a whole to fluorine active species.
It is a further object of the invention to provide a substrate holding apparatus at a low cost, thereby reducing the apparatus operating cost.